1. Field of the Invention
The present invention relates to an apparatus for recording and playing back digital data.
2. Description of the Prior Art
Analog recording has been heretofore used for a video cassette recorder (VCR). Where images are recorded in analog form and played back by VCR units, especially when dubbings are made, the image quality is deteriorated severely. Therefore, development of a VCR utilizing digital recording has been expected.
When an analog VCR unit is in the playback mode, signals distorted by noises and jitters are directly delivered from the VCR unit. If an edit, dubbing, or other operation is performed, distortions are accumulated. As a result, the playback image quality is deteriorated. However, in a digital VCR unit, an analog video signal and analog audio signals are sampled and converted into discrete quantized digital values, and then these digital values are recorded. Since the recorded values are discrete values, if the amount of noise is sufficiently small, then correctly recorded digital values can be easily obtained. Where erroneous digital values are obtained, they can be corrected by adding error correction codes during reading. In this way, in digital recording, image quality deterioration due to dubbing or the like can be suppressed greatly.
On the other hand, when an NTSC (the National Television Systems Comitee) signal that is broadcast by TV is digitized, the amount of data is increased, because when analog values are used, information at one point is expressed by one analog value, whereas when digital values are used, the same information is represented by plural data items. Therefore, use of digital VCR units is mostly restricted to broadcast applications.
In recent years, however, as the technique for compressing image information has evolved, it has become possible to compress video signals such that the amount of data is reduced by a factor expressed by one or two digits. Consequently, a consumer digital VCR unit which provides higher image quality and suffers from less image quality deterioration on dubbing compared with the conventional consumer analog VCR units can be accomplished.
Such consumer digital VCR machines utilizing the compressing techniques are capable of providing higher image quality than the conventional consumer analog VCR machines. Also, these digital VCR machines can be built in smaller size. Furthermore, it is considered that the consumer VCR machines can be fabricated in lower cost because they can be mass-produced.
Magnetic disks, magnetic tape, and others have been known as recording media for computers. Magnetic tape having a large storage capacity is used to back up data. As one kind of such magnetic tape, digital data storage (DDS) based on the format of digital audio tape (DAT) is known.